Antiskid systems for vehicles have been known for many years. Such systems have been used extensively in the trucking and railroad industries and are now being utilized on automobiles. However, the invention of interest herein, while being applicable to any vehicle having a braked wheel, is most particularly suited for implementation in the aircraft industry. In such industry, antiskid brake control systems are typically used to prevent skidding activity. It is understood that braking efficiency drops to nearly zero when the braked wheels lock-up or skid. Optimum braking efficiency is attained when braking is performed in such a manner as to allow the wheels to approach a skid without actually entering a skid. In other words, braking activity should occur near the peak of the mu-slip curve, as is now well known in the art. Further, present day antiskid brake control systems attain high efficiency by incorporating therein proportional, integral, and derivative inputs corresponding to the braking activity of the wheels.
It is further presented that modern day antiskid control systems, responsible for stopping large aircraft at high speeds while ensuring the lives of hundreds of passengers, must be quickly responsive to changing conditions, and highly accurate in operation. Further, such a system must be capable of adapting, through programming, to accommodate various aircraft characteristics such as are inherent with weight, landing speed, strut design, hydraulic system lag, and the like.
There have, of course, been many previously known antiskid brake control systems for aircraft. Typically, such systems have been of an analog nature, consisting of a plurality of discrete components. These discrete components have been responsible for monitoring wheel speed, converting the monitored signal to a varying DC level, and using such signal to modulate or adjust the maximum brake pressure availble to the pilot. However, the previously known analog signals have been inherently slow in response time, costly in production, requiring a large number of discrete components, each having its own inherent reliability limitations. Further, previously known analog systems have required specific dedicated circuitry which could be used for nothing other than antiskid brake control operations. In other words, the hardware provided for brake control is limited solely to the performance of that function.